The present invention relates to a magnetic recording device used as an external storage of a computer system.
In a conventional magnetic recording device as shown in FIGS. 4, 5 and 6, a base 101 includes a bottom plate 102 at a first side and a bottom plate 103 at a second side opposite to the first side. The bottom plate 102 is arranged at a slightly lower level than a level of the bottom plate 103. A base plate 104 made of a thin iron plate is arranged on the bottom plate 102. A resin layer (not shown) is arranged on the base plate 104 so that a circuit is printed on the resin layer and a circuit part 105 for driving a motor is arranged thereon. A printed board 106 for processing signals is arranged on a lower side of the bottom plate 103 so that a circuit part 107 for processing signals is mounted on the printed board 106. The circuits on the base plate 104 and the printed board 106 are connected to each other through a flexible printed board 108 extending over a staircase-shaped portion between the bottom plates 102 and 103. A spindle motor 109 is supported on the base plate 104. The base plate 104 supports a head supporting device 114 including a carriage 110 and a head arm 111 to hold a magnetic head 112 for a side 0 of a floppy disk and a magnetic head 113 for a side 1 of the floppy disk, a head positioning device 117 including a stepping motor 115 and a lead screw 116, and a disk loading device 122 including a driving member 118, a cartridge holder 119, a trigger lever 120 for operating also to open a shutter, and an inject lever 121.
As shown in FIG. 6, in the spindle motor 109, a housing 123 extends integrally from the bottom plate 102 of the base 101 to receive a ball bearing 124 for bearing an axial or thrust force and a radial force of the spindle 126 and an oleophilic-metal bearing 125 for bearing the radial force of the spindle 126 so that a spindle 126 is supported rotatably by the bearings on the base 101. A stator 127 is fixed to an outer periphery of the housing 123, and winding coils 128 are mounted along a circular line on the stator 127 with a substantially constant distance. A rotor 130 is fixed to a forward end of the spindle 126 through a bushing 129, and magnets 131 for generating magnetic flux between the magnets 131 and the stator 127 magnetized by the winding coils 128 are mounted on an inner surface of an outer peripheral portion of the rotor 130, so that the spindle 126, the rotor 130 and the magnets 131 are rotated for rotating the floppy disk in accordance with changes in magnetized portions of the stator 127 by the winding coils 128.
In the conventional spindle motor described above, an actual inclination of an longitudinal axis of the spindle 126 in relation to a desired rotational axis thereof is large when the spindle 126 is rotated on its rotational axis and a centrifugal force by unbalance of the rotor 130 and of the magnets 131 around the rotational axis and a magnetic force between the stator 130 and the magnets 131 are applied to the spindle 126. Alternatively, in order to make the inclination of the spindle 126 small, sizes and shapes of the spindle 126, the bearings 124 and 125 and an hole of the housing 123 must be very accurate and a distance between the bearings 124 and 125 must be large.